The long-term effect of ovariectomy on the quality and quantity of cancellous bone in young macaques

The effect of ovariectomy on the quality and quantity of cancellous bone using the young cynomolgus monkey was evaluated after a 2-year period. The bodies of the second lumbar vertebrae were analyzed for changes in bone mineral quality using density fractionation, chemical analysis, and X-ray diffraction techniques. Changes in bone tissue quality and quantity were evaluated using bone histomorphometry and image analysis. The experimental group (n=14) was made surgically menopausal (bilaterally ovariectomized), compared with intact controls (n=16), and then sacrificed after a 2-year period. There was a non-significant shift in the mineralization profile towards less dense bone in the ovariectomized (OVX) vertebrae compared with controls. Physical characteristics of the bone mineral in terms of crystal size or strain were unaffected by OVX. There was a parallel increase in mineral content with fractions of increasing density, however there was no difference in mineral content or the Ca/P ratio in each fraction between treatment groups. Histomorphometric analysis for structural parameters demonstrated no difference in bone volume between control and OVX groups. There was no significant change in trabecular width in the OVX vertebrae compared with controls. There was a significant increase in both osteoid volume and osteoid surface in the OVX vertebrae (P<0.001). Trabecular architecture as measured by image analysis was unchanged. There was a significant increase in eroded surface in the OVX vertebrae (P<0.03) compared with the controls. In conclusion, young, ovariectomized female cynomolgus macaques do not appear to be a useful animal model for the study of postmenopausal bone loss, however they may be a useful model to evaluate skeletal pathology which might be observed after surgical ovariectomy in young human females.